The purpose of this study is to assess the efficacy, safety, and how the body interacts with an investigational drug in pediatric patients with Crohn's disease who have not had success with other medications. After study participants are screened, if eligible, they will receive the study drug. The study drug in this study is called Upadacitinib. While Upadacitinib is FDA-approved for use in adults with Crohn's Disease, it is investigational for children with Crohn's Disease.